The oil and gas industry has for many years used hot tapping and stoppling techniques in order to provide localised isolation of a “live” section of pipe.
Hot tapping involves the fitting of a branch or tee connection to a live pipeline containing fluid at pressure. The connection may be welded or mechanically secured to the pipe, a valve being subsequently fitted to the connection. A tapping or drilling tool is then connected to the valve, the tapping tool being activated to pass through the open valve and drill through the pipe wall to create the branch. The tapping tool is configured to prevent leakage of fluid from the pipe. On completion of the drilling process, the tapping tool may be removed and the valve closed to complete the branch connection. Thus, fluid may be selectively directed via the branch connection. Alternatively, or in addition, tools may be inserted and/or removed via the hot tap connection to perform a variety of tasks within the pipe.
Where pipe isolation is required, a plug or stopple including a lip seal is inserted through the tap connection to provide uni-directional sealing isolation of the pipe inboard of the stopple. In order to apply a test pressure to test the integrity of the stopple seal a second opening is cut into the pipe at a location outboard from the first opening and a second plug or stopple put in place. A smaller third opening is drilled between the first and second openings to pressurize the isolated area between the first and second stopples, and thus pressure test the first or primary stopple seal, and also the second seal. This may only be achieved if the uni-directional lip seal arrangement of the second stopple is arranged against the prevailing pressure, that is in the opposite orientation to the first or primary seal. Thus, although two pressure-tested seals have been provided, only one, the primary seal, is effective against the isolated pressure.
In addition, each intervention into the pipe requires additional planning, setup and operation time resulting in increased costs for the operator.